Just some unsorted random ideas:
1. Would it be possible to lump some of the different MIPS variants
together more closely? In my dream world I could build one kernel that
would boot on every mips architecture. This way the work can be more
general. As it stands now, if you want Tx39 or Vr41 variants you're
working out of a different tree. With the number of SoC core products
coming out at present, this predicament is only likely to get more
serious. I know at one point in time you could boot a single ARM kernel on
several different systems and it would adapt it's processor specifics at
runtime. Such a design might help to bring the MIPS world together a bit.

There is at least a problem with endianess - I dont think there can be
a little and big endian kernel coexist in the same object or at least
not with major rework.

Well, yes that would be a problem, but at least within endianess, there's no
reason why the processor specific stuff can't be abstracted and attached at
runtime.

Why would you suggest having vr41 and TX39 in a seperat tree ? I had a
look in the linux-vr tree and i dont like some of their #ifdef spaghetti
stuff so i am currently working on TX39 stuff on top of the oss tree
which could be made cleanly. (Dont integrate all TX39 archs into one
subarch *grrr*)

It's kinda ugly, but some of that is that the original architecture didn't
scale to having many different target platforms. I think a little sane
multi-platform infrastructure would make things cleaner and better in the
future.